1. Technical Field
The present invention relates to an antenna device that is suitable for a wireless communication technology such as a keyless operation system for an automobile.
2. Description of the Related Art
Conventionally, antenna devices have been used that have an antenna component, such as a rod antenna and the like, that extends to the exterior in order to carry out wireless communication, such as in a keyless operating system for an automobile. However, in recent years, taking into consideration design characteristics, antenna devices that use an internal antenna have come to be used. However, because the antenna characteristics deteriorate due to the internal antenna accompanying the downsizing of the wireless devices, in Japanese Laid-Open Patent Application No. 2000-114865, for example, mobile communication that attains a high gain by using a hand strap has been proposed.
In this mobile wireless device, an internal antenna element is provided inside the case of the wireless device main body and a hand strap connecting portion in which a conducting ring-shaped hand strap is attached is provided in proximity to the internal antenna element. Thereby, the hand strap connecting portion and the internal antenna element are electromagnetically coupled, and a high gain is thereby obtained.
However, even in the conventional technology described above, the following problems remain.
Specifically, in the case in which a high gain is obtained by using an electromagnetically coupled hand strap, as in the Japanese Laid-Open Patent Application No. 2000-114865, there are the problems that the antenna characteristics become completely dependent on the hand strap, the design of the antenna becomes difficult, and stable antenna characteristics are difficult to attain. In addition, because the hand strap is connected to the ground (GND) of the wireless device, there is the inconvenience that the antenna gain of the internal antenna basically cannot be improved.
For example, as shown in FIG. 18A, in the case in which the wireless device has been downsized, as explained above, the area and volume of the internal antenna 2 on the substrate 1 and the circuit-side ground pattern 4 of the wireless circuit component 3 become small. In contrast, as shown in FIG. 18B, in order to widen the circuit-side ground pattern 4, a method can be considered in which the strap holder 5 or conducting hand strap 6 is electrically connected with the circuit-side ground pattern 4. However, because the original circuit-side ground pattern 4 is small, the antenna characteristics are unstable, the characteristics cannot be improved, and there is a concern that the wireless circuit component 3 may be damaged due to the influence of static electricity. Thus, as shown in FIG. 18C of the Japanese Laid-Open Patent Application No. 2000-114865, a method can be considered in which the conductive hand strap 6 and the circuit-side ground pattern 4 are electromagnetically coupled. However, although the problem of static electricity can be improved, the performance of the internal antenna 2 itself cannot be improved, and at the same time, the method is dependent on the condition of the hand strap 6 (the length and the arrangement state and the like), and the antenna characteristics become unstable. In this manner, in the conventional technology, an adequate antenna design and ground pattern design are difficult, and the improvement of the antenna characteristics is a difficult.
In consideration of the problems described above, it is an object of the present invention to provide an antenna device in which the deterioration of characteristics due to downsizing and thickness reduction are decreased, and at the same time, the characteristics of the internal antenna are improved to enable realizing a high gain and broad coverage.